Scientists say they are concerned at the rate at which methane in the atmosphere is now rising.

After a period of relative stagnation in the 2000s, the concentration of the gas has surged.

Methane (CH4) is a smaller component than carbon dioxide (CO2) but drives a more potent greenhouse effect.

Researchers warn that efforts to tackle climate change will be undermined unless CH4 is also brought under tighter control.

"CO2 is still the dominant target for mitigation, for good reason. But we run the risk if we lose sight of methane of offsetting the gains we might make in bringing down levels of carbon dioxide," said Robert Jackson from Stanford University, US.
Prof Jackson was speaking ahead of this week's American Geophysical Union (AGU) meeting in San Francisco where methane trends will be a major point of discussion.

With colleagues who are part of an initiative called the Global Carbon Project, he has also just authored an editorial in the journal Environmental Research Letters (ERL).

This paper makes a clarion call to the scientific community to address the knowledge deficit that surrounds CH4.

Quite why methane has suddenly spiked is not obvious. After barely moving between 2000 and 2006, the concentration in the atmosphere ticked upwards from 2007, and then jumped sharply in 2014 and 2015.

In those final two years, methane rose rapidly by 10 or more parts per billion (ppb) annually.

It is now just above 1,830ppb. By contrast, global CO2 emissions have flattened somewhat of late, giving hope that the rise in its atmospheric concentration (currently just above 400 parts per million) might also slow.

"Methane has many sources, but the culprit behind the steep rise is probably agriculture," Prof Jackson told BBC News.

"We do see some increased fossil fuel emissions over the last decade, but we think biological sources, and tropical sources, are the most likely."

Agricultural sources would include cattle and other ruminants, as well as rice paddies.

Emissions from wetlands are almost certainly a significant part of this story as well. But so too could be the role played by the chemical reactions that normally remove methane from the atmosphere.

One of the most important of these is the destruction process involving the so-called hydroxyl radical.

The concentration of this chemical species in the atmosphere might also be changing in some way.

According to the ERL editorial, there needs to be a particular push on understanding such methane "sinks".

CH4 is about 30 times better than CO2, over a century timescale, at trapping heat in the atmosphere.

Scientists use computer models to try to project how Earth will warm given a certain mix of gases, and right now methane's growth rate is close to a path that would take the world into a very challenging future.

"If we want to stay below two degrees temperature increase, we should not follow this track and need to make a rapid turn-around," said Dr Marielle Saunois from the University of Versailles Saint Quentin, France. She is the lead author on the ERL paper.

One development that should help scientists as they grapple with the methane issue is the launch of new satellites.

A number sensors are planned that will specifically target carbon molecules.

"I'm optimistic that the scientific community and the policymakers will be able to have better information. I'm optimistic because there are new satellites coming along that will give us the power to see methane concentrations all over the world on a regular basis," explained Prof Jackson.

"Methane is more difficult to study than CO2 because it's more diffuse, but I think we’re poised to make really good progress over the next few years."

Rapid rise in methane emissions in 10 years surprises scientists
Methane warms planet 20 times as much as similar CO2 volumes but lack of monitoring means scientists can’t be sure of sources
Fiona Harvey The Guardian 12 Dec 16;

Emissions of the powerful greenhouse gas methane have surged in the past decade, threatening to thwart global attempts to combat climate change.

Scientists have been surprised by the surge, which began just over 10 years ago in 2007 and then was boosted even further in 2014 and 2015. Concentrations of methane in the atmosphere over those two years alone rose by more than 20 parts per billion, bringing the total to 1,830ppb.

This is a cause for alarm among global warming scientists because emissions of the gas warm the planet by more than 20 times as much as similar volumes of carbon dioxide.

In the meantime, emissions of carbon dioxide – the main component of manmade greenhouse gases in the atmosphere – have been levelling off. The new research, published in the peer-review journal Environmental Research Letters, suggests that the world’s attempts to control greenhouse gases have failed to take account of the startling rises in methane.

The authors of the 2016 Global Methane Budget report found that in the early years of this century, concentrations of methane rose by only about 0.5ppb each year, compared with 10ppb in 2014 and 2015.

The scientists speculate that agriculture may be the main source of the additional methane that has been recorded. However, they cannot be sure of all the sources, owing to a lack of monitoring.

At least a third of methane comes from the exploitation of fossil fuels, including fracking and oil drilling and some coal mining, where methane is viewed as a waste gas and is frequently allowed to escape or, in some cases, flared off, which is less harmful.

Unlike carbon dioxide emissions, however, which have been tracked in various ways since the 1950s, emissions of methane are poorly understood and could represent a threat that scientists have still not accounted for.

For instance, the melting of the Arctic tundra releases methane as the vegetation underneath is gradually and sometimes suddenly exposed. This has been regarded by scientists as a potential “tipping point” whereby warming of the Arctic leads to greater releases of methane, therefore greater warming, in a runaway and uncontrollable cycle.

Comparison of methane over Alison Canyon, California, acquired 11 days apart in January 2016 by (left) Nasa’s Aviris instrument on an ER-2 aircraft at 4.1 miles altitude and (right) by the Hyperion instrument on Nasa’s Earth Observing-1 satellite in low-Earth orbit.

Although the world’s governments pledged at Paris last year to hold global warming to no more than 2C above pre-industrial levels, few have yet explained in detail how their intentions will be worked out. The president-elect of the US, Donald Trump, has also cast doubt on the US’s future participation in the emissions cuts required.

Robert Jackson, professor of earth system science at Stanford University, and a co-author of the paper, warned that methane should also be a key focus of attempts to control climate change.

“The levelling off we’ve seen in the last three years for carbon dioxide emissions is strikingly different from the recent rapid increase in methane. Unlike CO2, where we have well-described power plants, almost everything in the global methane budget is diffuse. From cows to wetlands to rice paddies [as well as other sources], the methane cycle is harder.”

“Why this change has happened is still not well understood,” added Marielle Saunois, assistant professor at the University of Versailles Saint Quentin, and a lead author of the paper. “For the last two years especially, the growth rate has been faster for the years before. It’s really intriguing.”

As well as measures that can be quickly implemented to prevent methane emissions from the fossil fuel industry, ways to cut emissions from agriculture are also being developed and implemented. New breeds of rice require less flooding in paddy fields, new feeds can cut down on emissions from cows, and there are methods of capturing methane from large agricultural barns where livestock are intensively reared. However, few of these are yet widely in operation.

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